The invention relates to a brake pressure control arrangement with an ABS and/or an ESP function for operating the brakes of a motor vehicle including pump units serving as boosters for the ABS and ESP functions and for the driver-initiated braking.
The arrangement comprises a hydraulic actuating device and a hydraulic receiver unit which is in communication with the hydraulic actuating device for operating the wheel brakes of the motor vehicle, and at least one pump unit which, by means of an automatic control device and control valves operated thereby, can be placed, when the hydraulic actuating device is actuated, in intervals into a first effective operating state wherein the receiver unit is, for pressure release, in communication with the suction side of the pump unit and into a normal operating state, wherein the receiver unit is in communication with the pressure side of the pump unit while the suction side of the pump unit is connected to the hydraulic actuating device. The hydraulic pressure at the hydraulic receiver is determined by the hydraulic fluid volume supplied to the hydraulic receiver unit, and a suction flow control valve is arranged between the actuating device and the pump and controlled by an automatic brake control arrangement.
Such a braking pressure control arrangement is the subject of DE 199 39 437 A1. This braking pressure control arrangement makes it possible with the use of a pump unit to provide for the receiver units hydraulic pressures which are substantially higher than the pressures generated by the hydraulic actuating device, that is, the pump is used as a pressure amplifier.
The first pump-effective operating state serves to rapidly reduce the pressure at a hydraulic receiver if a wheel blocks during a braking procedure, so that the wheel is again rotated and can transmit correspondingly higher side guide forces. The first pump-effective operating state is consequently mainly used for the anti-blocking control of vehicle wheels.
Furthermore, with the brake pressure control arrangement according to DE 199 39 437 A1 also a drive wheel slip control can be provided. In this case, the pump unit can be controlled at intervals, when the actuating device is not operated in a second pump-effective state wherein the hydraulic receiver units are placed in communication with the pressure side of the pump unit. A spinning wheel can, in this way, be braked down.
DE 199 39 437 A1 discloses a brake pressure control arrangement wherein a pressure limit valve is arranged between the pressure side of the pump unit and the hydraulic actuating device, which pressure limit valve is controlled by a piston arrangement depending on the pressure provided by the hydraulic actuating device, that is, the hydraulic actuating device pressure determines the maximum pressure provided at the pressure side pump unit.
For this reason, the pressure limiting valve must be arranged in series with a shut-off valve which is operated by the control arrangement if the driving wheel slip control mentioned earlier is to be ensured. During driving wheel slip control the shut-off valve is automatically closed, so that, at the receiver units or, respectively, the pressure side of the pump unit, a high pressure can be provided although the pressure limit valve has only a very small opening pressure when the actuating unit is not operated that is the pressure supplied by the actuating unit is very small.
DE 197 56 248 A1 discloses for example a brake pressure control system wherein the vacuum generated in the internal combustion engine of a motor vehicle is utilized for generating the auxiliary forces. This arrangement also permits the generation of high hydraulic pressures for actuating the vehicle brakes with comparably small actuating forces applied by an operator.
DE 197 16 404 C1 discloses another possibility to generate at the receiver units a hydraulic pressure which is high in comparison with the operating force applied at the actuating unit. In accordance with this publication, the actuating unit includes a stepped piston which, with a first piston area is disposed in a first operating cylinder and with a second piston area is disposed in a second cylinder for the displacement of the hydraulic fluid therein. Both cylinders are in communication in parallel with respective receiver units of the wheel brakes (wheel cylinders) wherein a pump can be provided in the communication lines between the two cylinders in such a way that the pressure in one of the cylinders can be reduced. In this way, the actuating force applied by the operator is mainly effective as a high pressure in the other cylinder, that is, the actuating force is transmitted to a relatively small piston area so that a relatively high hydraulic pressure is generated in the receiver units generating a high brake force.
It is the object of the present invention to provide a brake pressure system of the type initially described however of a more simple design.